Even if you think you can play guitar perfectly, there's always room for improvement. Mastering guitar techniques is essential and can make your songs and riffs much more interesting.

Picking:

Alternate Picking

Alternate picking is essential to learn... Unless you're James Hetfield... Alternate picking is when you alternate between down strokes and up strokes, this technique is very important and after mastering this, you will notice how much faster you can play.

Tremolo Picking

Tremolo picking is almost the same as alternate picking, it's just faster. If you don't understand just listen to an Eddie Van Halen solo.

Palm Muting

Rest the palm of your picking hand lightly over the strings near the bridge saddle.

Appreggiated Chord

Instead of playing the chord, pick each note of the chord moving from the top of the chord to the bottom.

Fretting Hand:

Hammer-On and Pull-Off

Pick the first note then hammer down on the string for the second note. When hammering-on pretend that you're trying to poke a hole in the neck. A good example of this technique is the intro of "Thunderstruck" by AC/DC.

Note Trills

Rapidly alternate between 2 notes using hammer-ons and pull-offs.

Slides

Pick one note then keep slide your hand along the neck to the next note, repick.

Fret Hand Muting

Place your fretting hand lightly over the neck and rake the strings, don't press too hard or the notes will sound, and don't press too gently or it will come out as a harmonic.

Bending And Vibrato:

Bend And Release

Pick a note, bend up to the desired pitch, then release gently but still hold the note or it won't sound the way you want it to.

Pre-Bend

Bend a note silently, but don't pick it until you want it to be heard. After picking it slowly release it.

Quarter-Tone Bend

Bend a note as you usually would but don't bend it all the way, bend it halfway, this is also referred to as a 'Blues Curl'.

Vibrato

A technique that Angus Young can; t get enough of. Pick a note then instead of letting it ring or muting it, do very small bends and releases.

Harmonics:

Natural Harmonics

Press down on the frets very gently, not too gently and not too hard. As the note sounds, move your finger away.

Pinched Harmonics

As you pick a note, dig into the string and 'pinch' it between your thumb and pick. You will notice that the pitch of the note depends on how close your picking hand is to the bridge, if it's close to the bridge, it will sound much more high pitched. This technique takes a lot of patience to learn but sounds really cool once it's been mastered, if you don't believe me, ask Zakk Wylde.

Tapped Harmonics

Place your finger on the desired note and sound it with a quick tap on the fret shown in the tab.

Vibrato/Whammy Bar

Whammy Bar bends

Pick the chosen note, then raise your whammy bar and lower it to the pitch which should be indicated on the tab.

Scoop And Doop

Scoop: Depress the bar just before picking the note and release.
Doop: Lower the bar after picking the note.

Gargle

Pick the note then 'flick' the bar.

Whammy Bar Vibrato

Gently rock the bar to bend the pitch up and down, repeat. This sounds similar to a fret hand vibrato.

Other:

Pick Scrape

Drag the edge of your pick up or down the strings, this works better on the lower strings.

Violining

Turn your volume down, then play a note or chord, then turn your volume up, a great example of this is before the second solo of "Estranged" by Guns N' Roses where Slash pre-bends notes then violins them in as he releases the bend, which sounds like a whale or a dolphin.

Feedbacking

Not sure if this is a technique, but it sounds really cool. To do this you need to be playing into a high-gain amplifier, play a note and give it a vibrato, then get your pickups as close to your amp as possible, if it doesn't work immediately, turn up your volume or gain. If you have a noise gate, then turn it off when you want to do this.
I'm not sure what this one's called but it sounds really cool!
This only works if you have a guitar with 2 volume pots. Set your bridge pickup's volume on full and your neck pickup's volume on 0. Switch to the bridge pickup then play a note or chord, then rapidly switch between the 2 pickups, the effect is really cool. WARNING: Don't switch between them too fast because your pickup switch might just break off! Listen to the intro to the live version of "Crazy Train" with Randy Rhoads, he bends a note then does this.
Thanks, I hope this helps!

It's funny I get the feeling a lot of people read this list and just say "Duh" but honestly, how many of you use anything like 1/4 bend tone or violining? I only know about them because I think 1/4 tone bends sound AMAZING to end or start a phrase with, and I learned violining from a Muse tab book.
Great article.

How do you whammy without a bar? I've always bent the neck forward/backward to try and get the sound on my les paul. Works okay for lower notes/chords like an open E for example, starts to sound sucky after the 6th fret or so.
People tell me i shouldn't do this though as it can warp the neck? Is there another way to do them on a fixed bridge?

Sweep picking, string skipping, trilling while using the tremolo arm, playing the strings in unorthodox places, utilizing your guitar's controls, expression pedals, effects pedals in general, using the guitar as a percussive instrument, hybrid picking, fingerstyle, slide guitar, playing with a power drill?